This invention generally relates to a heat exchanger tube of the inner finned type which is useful in making a heat exchanger coil of the continuous plate finned type for exchanging heat between flowing streams of gas of different temperatures.
Heat exchanger metal tubing of the inner finned type and their method of manufacture are known and have been described in the literature, for example U.S. Pat. No. 3,662,582. An inner finned tube may be formed utilizing brazing or otherwise joining inserted fins into the inner wall of a tube blank. It also may be formed by displacing the material from the wall of the blank into the grooves on a mandrel so that the inner fins are formed integrally with the wall. Such a method decreases the wall thickness of the tube and also causes an elongation of the tube. Other heat exchanger tubing having differing configurations with or without external fins are shown in U.S. Pat. Nos. 3,847,212, 3,273,599, and 3,796,258.
Many other configurations of inner finned or externally finned heat exchanger tubes have been used for specific requirements. However, where two flowing streams of gas are utilized for the exchange of heat it generally requires a heat exchanger coil of relatively large surface area in order to obtain the necessary degree of heat exchange between such gases. To obtain the most compact heat exchange configuration, both the inside and outside tube surfaces must contain fins. Heat exchangers, as is shown in U.S. Pat. No. 3,796,258, which utilize an array of parallel tubes having no internal fins and positioned through continuous plate fins do not increase the internal surface area of the tube.